Can I use comments inside a JSON file?

No, standard JSON does not allow comments according to the official JSON specification (ECMA-404). Any comment-like text in a JSON file will usually cause parsing errors in strict JSON parsers.

JSON (JavaScript Object Notation) is one of the most popular data interchange formats used by developers worldwide. Lightweight, easy to read, and well-structured, JSON enables seamless data exchange across different systems and programming languages. When developers first encounter JSON, a common question arises: “Can I add comments to my JSON files?” Let’s explore this in detail.

Why JSON Doesn’t Support Comments

JSON was designed to be a simple data exchange format, free from the complexities of a typical programming language. The primary aim was to keep JSON lightweight and universally compatible, so it omits features like comments.

Although it might be tempting to annotate your JSON for clarity, these annotations could break the format. If your JSON needs to travel across multiple services, each with its own JSON parser, you risk errors if your data isn’t strictly compliant.

Common Workarounds

1. Use a JSON Superset
   Some developers use “JSONC” (JSON with Comments). Tools like certain VS Code extensions or specialized libraries can parse JSONC by removing comments before handing over valid JSON to applications. However, JSONC is not an official standard.

2. Add Descriptive Keys
   Instead of writing comments, you can create fields that explain data. For example:

   {
     "user_name": "JohnDoe",
     "_comment_for_user_name": "Keep this name consistent across all systems"
   }

   While this isn’t elegant, it ensures that data remains strictly valid JSON.

3. Maintain Documentation Elsewhere
   If you want to document your JSON structure, keep a separate README or documentation file. This eliminates any risk of parse-time errors while still providing clarity.

Best Practices

• Stay Standard-Compliant: Whenever possible, stick with official JSON specifications—especially for production systems.
• Use Comments Only During Development: If you’re using a specialized environment that ignores or strips out comments, ensure that your final JSON files remain comment-free when deployed.
• Leverage Other Formats for Complex Configurations: If your use case requires extensive configuration details and annotations, you might consider YAML, TOML, or even JavaScript files. These formats can support inline comments in a more robust way.

Mastering JSON and JavaScript Fundamentals

To work with JSON effectively, it helps to have a solid grasp of JavaScript fundamentals. If you’d like to deepen your knowledge, Grokking JavaScript Fundamentals by DesignGurus.io provides a comprehensive look at the core principles of JavaScript, which underpins JSON. By understanding how JavaScript objects relate to JSON, you’ll become more proficient in crafting data structures that are both clean and efficient.

Final Thoughts

While JSON doesn’t natively support comments, there are several ways to tackle documentation or extra annotations without breaking the official specification. Whether you choose to use a superset like JSONC, store comments as separate fields, or opt for an external documentation approach, it’s best to keep your production JSON files strictly valid.

Ultimately, it’s all about balancing clarity and standards compliance. And if you want to ensure your JavaScript and JSON knowledge is rock-solid, don’t forget to explore Grokking JavaScript Fundamentals for a deeper dive.